Many consumer products and other electrical devices need to convert an alternate current (AC) power input provided by electrical mains into a direct current (DC) power output that is required by the device's circuitry. An external AC power adaptor is often used for such a purpose. In addition to performing its primary function of converting an AC input into a DC output having characteristics suitable for the device's circuitry, an external AC power adaptor provides several design advantages over an internal AC power adaptor.
For example, safety concerns and/or regulations dictate that the power circuitry of an AC power adaptor be housed in an appropriately secure manner to reduce the risk of user injury. Typically, any component that can become energized with AC power needs to have a secure housing that protects against inadvertent user contact with the energized component. By moving such power circuitry outside of a device, the device itself may not need to incorporate the same level of safety features because the device only uses the DC output of the adaptor. In addition, the device may be made smaller and lighter because the size and weight of the AC power adapter, along with its housing or other safety features, is located outside of the device.
FIG. 1 illustrates a cross-sectional view of an external AC power adaptor that is configured according to the prior art. In FIG. 1, external AC power adaptor 10 receives an AC input by way of wire 5. Power circuitry 20 converts the AC input to a DC output that has characteristics (e.g., 12V, etc.) that are suitable for a device to which power is being supplied (not shown in FIG. 1 for clarity). The DC output is transmitted to a device by way of wire 11. It will be appreciated that an embodiment is equally applicable for use in connection with any type of electrical device that requires an external AC power adaptor.
It can be seen in FIG. 1 that power circuitry 20 is located within compartment 22. Compartment 22 is bounded by portions of housing 24 and heat transfer plate 26. To provide cooling for power circuitry 20, the circuitry 20 is thermally coupled to heat transfer plate 26 using a thermally-conductive adhesive or the like. Housing 24 may be formed such that one or more openings 28 may be present to allow air within compartment 32 to circulate across heat transfer plate 26 and therefore cool power circuitry 20. To provide for enhanced cooling, heat sink 34 is thermally coupled to heat transfer plate 26. In addition to, or in place of, heat sink 34, fan 36 may be located within compartment 32 to provide forced air cooling, represented in FIG. 1 by air flow A.